Genetics

• Chapter Eight: Reproduction

• Chapter Nine: Heredity

• Chapter Ten: The Code of Life

Chapter Nine: Heredity

• 9.1 Traits

• 9.2 Predicting Heredity

• 9.3 Other Patterns of Inheritance

9.3 Other Patterns of Inheritance

• Plant and animals have thousands of genes.

• Some have patterns of inheritance that are different from the ones Mendel discovered.

• We have learned that some traits do show complete dominance.

9.3 Male or Female?• In humans, sex is

determined by the last pair of chromosomes.

• Sex chromosomes carry genes that determine whether an individual is female or male. (Mendel’s peas did not have sex chromosomes.)

9.3 Male or Female?• Females produce

eggs with only X chromosomes.

• Males produce sperm with either an X or a Y chromosome.

• What is the probability for having a girl or boy child?

9.3 Incomplete Dominance

• Sometimes one allele isn’t completely dominant over the other.

• Cross a true-breeding, red-flowered snapdragon with a true-breeding, whitewhite -flowered snapdragon and you end up with pink snapdragons!

x

9.3 Incomplete Dominance

We use these letters:

is a red flower

is a white flower

is a pink flower

What would happen if 2 PINK snapdragons are crossed?

9.3 Codominance• In codominance, an organism has two different

alleles of a gene and shows both phenotypes at the same time.

9.3 Multiple alleles

• Multiple alleles are also common in organisms.

• In humans for example, three alleles determine blood type (A, B, and O).

9.3 Polygenic Traits

• Inherited traits that are determined by more than one gene are called polygenic traits.

• Feather color in parakeets is determined by two genes.

• One gene controls yellow color and the other controls blue color.

9.3 Environmental factors

• Environmental factors may also influence traits.

• For instance, in certain reptiles, sex is determined by temperature.

• During development in the egg, higher temperatures favor the production of males.

Activity

• A pedigree, or family tree, is a diagram that shows the generations of a family.

• Use the pedigree below as a model for this activity.

Making a Pedigree

Health Connection

• Normally, red blood cells are round and disk-shaped.• With sickle cell anemia the red blood cells are sickle-

shaped.

An Inherited Disease